SB aluminum 1 piece mains/girdle

[gzig5]

Would one made of steel expand at the same rate as the cast iron block? My design would be a lot different, it would not have the rail around the pan. Been thinking of this for 6 months now.

I would be using Durabar if I had my preference. It would probably need to be spliced together rather than carving it out of a single block. That would have some benefits, especially for cost but might make the design more complicated to keep the stability. After Durabar, some sort of alloy steel like Milodon uses.
I was looking at making main caps for a 340 block and nobody seemed to think aluminum was a good idea but it is used on big block caps routinely.

 

[justinp61]

Even if it helps IMHO it’s a bandaid.

 

[CNC-Dude]

I would be using Durabar if I had my preference. It would probably need to be spliced together rather than carving it out of a single block. That would have some benefits, especially for cost but might make the design more complicated to keep the stability. After Durabar, some sort of alloy steel like Milodon uses.
I was looking at making main caps for a 340 block and nobody seemed to think aluminum was a good idea but it is used on big block caps routinely.

It's no different than Rodeck or Donovan aluminum blocks having steel main caps. The different expansion rates are a non-issue and never have been. The same can be said about aluminum heads on an iron block and how it might affect stress on the head studs or bolts once it reaches operating temps. These are things that just dont have any detrimental effects on an engine.